This invention relates to computer printers, and is particularly concerned with improved means for enhancing the performance, reliability and maintainability of high-speed line printers.
Line printers are peripheral to computer systems, providing primarily for alphanumeric "hard copy" output. Printing speed is usually very high, ranging from 130 to 280 lines per minute, for example. This high speed is made possible largely by the bidirectional movement of the print head.
Line printers, once turned on, are expected to operate for long periods unattended, and with high reliability. The print medium, such as the fan-fold, edge-punched continuous form, is usually loaded in large quantities. Any necessary adjustment such as for print medium thickness, drive belt tension, or print head to platen parallelism, should be such as to be accomplished quickly and easily, and without the need for special tools or skills.
Paper thickness adjustment in the Xerox Model 630 Communications Terminal is accomplished by means of a two-position "multicopy" lever which also adjusts for print intensity. Setting the lever in its upper position moves the carriage close to the platen, and actuates a switch for the proper setting for light and medium weight paper, and form sets of up to two carbon copies. For heavier paper, or form sets of up to five copies, the multicopy lever is set to its lower position. This rocks the carriage away from the platen slightly, and deactivates the switch to enable an increased print density. The platen of the Model 630 is similar to that of a standard typewriter in that it comprises a hard rubber roller. Paper is inserted behind the platen while the platen is turned manually to bring the paper around and up in front of the platen.
In the Diablo Model 1640 line printer, adjustment for paper thickness is made by moving the roller platen toward and away from the print head, much the same as it is done in the standard typewriter.